Conventional clutches are used in all kinds of drives in which a disconnection of the drive train during operation is envisioned. They can be used in all types of vehicles, as well as in stationary plants that provide disengagement in operation. Clutches of this kind are switchable, so that they can be switched between an engaged and a disengaged state during operation. Such clutches mostly have disk-shaped coupling surfaces, which transmit power between the two sides of the clutch through mutual engagement in engaged or locked state. In the process, one side can be provided with a torque from a drive, while the other side provides for the transmission of the torque to an output. This state is, however, not fixed. Modern transmissions can, according to the gear that is selected, lead to different torques being transmitted via the same clutch, even originating from different sides.
Thus, in each case according to the use of the clutch, a plurality of power paths can be transmitted from a connected transmission via the clutch. Here, even the direction of the power flow can be changed via the clutch, so that an input or an output of the clutch can alternate in each case according to operating state.
In an open or disengaged state, the coupling surfaces or coupling elements are spaced apart by a clearance. In most cases, such clutches are designed as wet clutches and run in a fluid for lubrication and heat dissipation. In order to keep the locking operations during operation brief and also to design the installation dimensions of such clutches to be small, the coupling elements are spaced apart in the disengaged state, but only with a minimal clearance so that a switching can take place rapidly and with low travel.
Conventional coupling elements are in operational connection with the sides of the clutch that are assigned to them even in disengaged state. This causes the coupling element to continue to rotate at the rotary speed of the relevant associated side of the clutch even when the clutch is disengaged. Because of this, in the disengaged state, the coupling elements are at a short spatial distance from each other and rotate in opposite directions. Because of the rotation of the coupling elements in the oil bath of the clutch, shear forces arise due to friction with the fluid. These shear forces cause a drag and thus a power loss of the clutch in the disengaged state if power is applied to at least one side of the clutch. This leads to heating of the liquid and to power losses in the drive. Not only can there be oxidation processes in the oil due to the heating, but there can be an increasing power loss due to which fuel consumption values for the drive rise significantly while at the same time less power is available for operation.